sch_dsmark: update backlog as well

[ Upstream commit bdf17661f63a79c3cb4209b970b1cc39e34f7543 ]

Similarly, we need to update backlog too when we update qlen.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: open-code qdisc_qstats_backlog_{inc,dec}()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc net/sched/sch_dsmark.c
Simple merge